The present invention relates to an electronic endoscope system that is adapted to observe a fluorescence image of autofluorescence emitted from a body cavity wall irradiated with excitation light, as well as a normal image of the body cavity wall illuminated with white light, on a display device such as a monitor.
An example of such an electronic endoscope system is disclosed in Japanese Patent Provisional Publications No. HEI 9-066023. The system disclosed in this publication includes a first solid-state imaging device that takes a fluorescence image, and a second solid-state imaging device that takes an RGB color image in accordance with a frame sequential-method. In the system, signals outputted film the first and second solid-state imaging devices are processed by video circuits for fluorescence images and for normal images, respectively. The signals are then synthesized by an image synthetic circuit, and are displayed on a monitor device. According to the operation of a display image selector switch, one of the two kinds of images or both is displayed on the monitor device.
Another example is disclosed in Japanese Patent Provisional Publication No. P2003-33324A. FIG. 12 shows a block diagram of the system that is illustrated in FIG. 16 of this publication. The system disclosed in this publication includes (see FIG. 12) a first lamp 124 that emits illuminating light for normal observation and a second lamp 125 that emits excitation light, and either one of the two kinds of light is selectively introduced into a light guide 133 by changing the position of a movable mirror 128. Image signals captured by CCD 137 are stored in a first memory 141 and a second memory 142, and are then displayed on a Hi-Vision monitor 115 through a display location selector circuit 144. When a selector switch for displaying two images (hereinafter, referred to as a two-image-display switch) is turned ON, a normal image and a fluorescence image are displayed on the Hi-Vision monitor 115, simultaneously.
Since the image data captured by the imaging device has an aspect ratio (for example, 4:3) equivalent to the aspect ratio of the monitor's display area, the display area is effectively used when either one of the normal image and the fluorescence image is separately displayed without any special processing being applied. However, when both kinds of images are displayed side by side as described above, the display area is not effectively used, and each image becomes small. Consequently, it is difficult to make a diagnosis with checking the details of the image. The latter publication discloses a technology of maintaining each image size by using the Hi-Vision monitor that has a larger aspect ratio of the horizontal length of the display area to the vertical length thereof. However, if such a relatively expensive Hi-Vision monitor is used, the entire system cost will arise.